This application claims the priority of German Patent Application No. 197 35 721.0, filed Aug. 18, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process and an arrangement for controlling the fuel injection quantity for an internal-combustion engine in a vehicle.
Such a process and such an arrangement are known, for example, from the current four-cylinder internal-combustion engines in BMW vehicles. These BMW vehicles have an electronic internal-combustion engine control unit with a Motorola processor arrangement (such as a 68333 or 68336) which contains two different, mutually communicating processors (CPU (central processing unit), TPU (time processing unit)). As the first processor of this processor arrangement, the CPU carries out, in particular, computing-time-intensive functions, whereas, the TPU, as the second processor of this processor arrangement, carries out real-time-critical functions, in particular, crankshaft-synchronous control functions. Both processors may be equipped wits application-specific software programs.
For controlling the fuel injection quantity, which is carried out preferably in a cylinder-selective or sequential manner, the CPU transmits a defined fuel injection time and a defined injection end angle of the crankshaft in each case for a certain cylinder to the TPU. The TPU detects the actual angle of the crankshaft. As a function of the actual angle of the crankshaft, of the defined fuel injection time and of the defined injection end angle, the TPU determines the injection starting angle of the crankshaft required for this purpose or the required injection starting point in time. If the determined starting point in time has been reached or the actual angle corresponds to the determined required injection starting angle, the TPU carries out the injection in a time-controlled manner by triggering the injection valve, which is assigned to a certain cylinder, for the defined fuel injection time without further taking into account the actual angle of the crankshaft.
In this known process, the actual injection end angle after the emission of the defined fuel injection time usually corresponds with a very high precision to the defined injection end angle if the angular crankshaft speed or the rotational speed of the internal-combustion engine remains constant during the injection. If, however, particularly in the case of starting operations, there are strong rotational speed fluctuations, then the actual injection end angle will frequently deviate considerably from the defined injection end angle. If, in the case of the known process, the rotational speed is increased for a short time during the injection, the deviation of the actual injection end angle from the defined injection end angle is ignored because, in this case, the defined injection end angle is situated before the actual injection end angle. However, if, during the injection for the defined fuel injection time, there is a slowing of the rotational speed, then the actual injection end angle is before the defined injection end angle. In the case of the known process, the injection is started here again for the already previously defined fuel injection time if, after a defined waiting time, the defined injection end angle has not yet been reached. In the event of rotational speed fluctuations, this approach frequently results in unnecessary double injections.
It is therefore an object of the present invention to improve upon a process of the above-mentioned type such that unnecessary double injections and therefore an unnecessary fuel consumption are avoided.
This object is achieved by a process for controlling the fuel injection quantity for an internal-combustion engine in a vehicle by means of an electronic control unit in which the actual angle (KW.sub.-- actual) of the crankshaft is detected. As a function of the actual angle (KW.sub.-- actual), of a defined fuel injection time (ti; t.sub.-- real) and of a defined injection end angle KW.sub.-- des), the required injection starting angle (KW.sub.-- start) of the crankshaft or the required injection starting point in time (tiS) for a certain cylinder is determined. The injection is carried out in a time-controlled manner by triggering the injection valve (EV), which is assigned to the certain cylinder, for the defined fuel injection time (ti) to an actual injection end angle (KW.sub.-- end) In the control unit, while maintaining the defined injection end angle (KW.sub.-- des; 15), a short pulse t.sub.-- short) is defined as the additional injection time (ti) for the certain cylinder if the actual injection end angle (KW.sub.-- end; 9) is before the defined injection end angle (KW.sub.-- des; 15).
An arrangement for achieving this object in an internal-combustion engine in a vehicle with an electronic control unit has two mutually communicating processors (TPU, CPU), in which, for a certain cylinder, a first processor (CPU) transmits a defined fuel injection time (ti; t.sub.-- real) and a defined injection end angle (KW.sub.-- des) of the crankshaft to the second processor (TPU). The second processor (TPU) detects the actual angle (KW actual) of the crankshaft. The second processor (TPU), as a function of the actual angle (KW.sub.-- actual), of the defined fuel injection time (ti) and of the defined injection end angle (KW des), determines the required injection starting angle (KW.sub.-- start) of the crankshaft or the required injection starting point in time (tiS). When the injection starting angle (KW.sub.-- actual=KW start) is reached, the injection is carried out in a time-controlled manner by triggering the injection valve (EV), which is assigned to the certain cylinder, for the defined fuel injection time (ti). The second processor (TPU) transmits the actual injection end angle (KW.sub.--end; 9) or the injection end point in time (tiE) and the actual angle (KW.sub.-- actual) to the first processor (CPU). The first processor (CPU) compares the defined injection end angle (KW.sub.-- des; 15) and the actual injection end angle (KW.sub.-- end; 9) with one another. If the defined injection end angle (KW.sub.-- des; 15) is after the actual injection end angle (KW end; 9), the first processor (CPU) defines to the second processor (TPU), while maintaining the previously defined injection end angle (KW.sub.-- des; 15), a short pulse t.sub.-- short) as the additional fuel injection time (ti).
The defining of an additional short pulse as an additional fuel injection time while maintaining the previously defined injection end angle if the actual injection end angle at the end of the injection for the previously defined fuel injection time is before the defined injection end angle is essential for the present invention. When a short pulse is defined, the approach is conventionally such that, as a function of the actual angle of the crankshaft, of the defined fuel injection time--here, in the form of the short pulse--, and of the defined injection end angle, the required injection starting angle of the crankshaft or the required injection starting point in time is determined again. In this case, the length of the short pulse is determined such that no rotational speed change can occur or be detected during the time of the short pulse. Thus, it is ensured that, at the end of the fuel injection time in the form of the short pulse, the actual injection end angle is necessarily equal to the defined injection end angle.
According to an advantageous further development of the invention, the injection valves are switched off at least for the duration of the short pulse so that a fuel injection time in the form of the short pulse is only virtually defined in the control unit without in fact triggering a superfluous fuel injection.
Thus, on the basis of the known process and the known arrangement, using the process according to the present invention and using the arrangement according to the present invention, a reliable rotational speed synchronization is carried out without causing a superfluous fuel consumption.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.